A prenuptial agreement is only valid if it is completed prior to marriage. After a couple is married, they may draw up a post-nuptial agreement. In the United States, prenuptial agreements are recognized in all fifty states and the District of Columbia.
Osmosis - the diffusion of water (across a membrane) Water will move in the direction where there is a high concentration of solute (and hence a lower concentration of water. A simple rule to remember is: Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction.
In biological systems, osmosis is essential since many biological membranes are semipermeable, and it leads to different physiological effects. For example, when an animal cell is exposed to a hypertonic surrounding (or lower water concentration) the water will leave the cell causing the cell to shrink.